CN113675477B - Asymmetric lamellar polymer matrix composite solid electrolyte suitable for 4.5V all-solid battery, and preparation method and application thereof - Google Patents
Asymmetric lamellar polymer matrix composite solid electrolyte suitable for 4.5V all-solid battery, and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses an asymmetric lamellar polymer matrix composite solid electrolyte suitable for a 4.5V all-solid battery, and a preparation method and application thereof. The method comprises the following steps: adding polyethylene oxide, polyvinylidene fluoride and lithium bistrifluoromethane sulfonyl imide into N, N-dimethylformamide, and adding an oxide-based ion conductor and a functional lithium salt additive to obtain a positive electrode layer; adding polyethylene oxide and lithium bis (trifluoromethanesulfonyl) imide into N, N-dimethylformamide, adding an oxide-based ion conductor and a functional lithium salt additive to obtain a negative electrode layer, and combining to obtain the composite solid electrolyte. In the invention, different film forming additives are added in the electrolyte layer at the positive electrode side and the electrolyte layer at the negative electrode side, so that stable solid electrolyte films can be formed on the surfaces of the positive electrode and the metal lithium negative electrode respectively. The layered polymer-based solid electrolyte can be used in a 4.5V high-voltage all-solid-state lithium battery, and enables the all-solid-state battery to have double-interface stability, and to show high rate capacity and ultra-stable cycle performance.
Description
Technical Field
The invention belongs to the technical field of solid-state lithium batteries, and particularly relates to an asymmetric layered polymer-based composite solid-state electrolyte suitable for a 4.5V all-solid-state battery, and a preparation method and application thereof.
Background
Compared with the traditional liquid lithium ion battery, the all-solid-state lithium metal battery has excellent safety performance, and the used solid electrolyte has the characteristics of non-volatilization, non-leakage, non-combustibility and the like. In addition, the high-voltage all-solid-state lithium metal battery assembled by using the high-voltage active material as the positive electrode also has an advantage in energy density over the conventional liquid ion battery. Therefore, high voltage all-solid-state lithium metal batteries are considered to be one of the most promising next-generation energy storage devices. Nevertheless, the development of high-voltage all-solid-state metal lithium batteries is currently faced with a number of problems such as instability of the positive electrode-electrolyte interface, the negative electrode-electrolyte interface, and the electrolyte itself.
The solid-state electrolyte, which serves as a core in the solid-state battery, has properties that directly determine the performance of the assembled solid-state battery. Solid state electrolytes can be divided into three general categories: inorganic solid electrolyte, organic polymer solid electrolyte, and organic-inorganic composite solid electrolyte. The organic-inorganic composite solid electrolyte thus has both high ionic conductivity and high chemical stability of the inorganic solid electrolyte, and the organic polymer solid electrolyte has the characteristics of mechanical softness, easy processing, mass production and the like. The use of organic-inorganic composite solid-state electrolytes in high-voltage solid-state batteries requires a series of problems to be solved, such as electrochemical stability of the electrolyte itself at high voltages, compatibility of the electrolyte with the positive electrode, and compatibility of the electrolyte with the metallic lithium negative electrode, among others. It is noted that the corresponding solutions to these problems are not identical.
Patent application CN111969247a discloses a solid electrolyte for in-situ protection of metallic lithium negative electrode and a preparation method thereof. According to the method, protective lithium salt is used as an additive, so that SEI film can be continuously generated on the surface of the metal lithium negative electrode, and the growth of lithium dendrite can be effectively inhibited.
Patent application CN109301317B discloses a method for preparing a high-pressure resistant solid polymer electrolyte. According to the method, the inorganic nano wires or nano particles are used as the filler, so that the high-voltage resistance of the solid polymer electrolyte is improved, and the high-voltage ternary positive electrode material can be matched.
These studies have demonstrated that specific problems, such as improvement of high-voltage resistance of the composite electrolyte and compatibility with metallic lithium negative electrodes, can be solved by specific measures. However, these improvements are limited and do not allow for modification of the electrolyte while also stabilizing the "positive electrode/electrolyte" and "negative electrode/electrolyte" double interfaces. In view of the difference in the performance requirements of the solid state electrolyte on the positive and negative sides, it is desirable to develop an asymmetric composite solid state electrolyte structure that meets both the positive and negative side requirements; meanwhile, the targeted lithium salt film forming additive is adopted on the positive electrode side and the negative electrode side, so that the modification of the solid electrolyte and the stability of the double interfaces of the positive electrode-electrolyte and the negative electrode-electrolyte are realized. This is of great significance for the application of high-voltage all-solid-state lithium metal batteries.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide an asymmetric lamellar polymer matrix composite solid electrolyte suitable for a 4.5V all-solid battery, and a preparation method and application thereof.
The preparation method provided by the invention can prepare an asymmetric lamellar polymer matrix composite solid electrolyte structure, and can simultaneously meet different requirements of the positive electrode side and the lithium negative electrode side on the polymer matrix solid electrolyte. Meanwhile, a functional lithium salt additive which is easy to be oxidized and decomposed into a film is added on the positive electrode side to form a stable positive electrode/electrolyte interface; the negative side is added with a functional lithium salt additive which is easy to reduce and form a film so as to form a stable 'negative electrode/electrolyte' interface. The asymmetric lamellar polymer matrix composite solid electrolyte prepared by the method can be used in a 4.5V high-voltage all-solid-state lithium battery, and the assembled LFMP matrix all-solid-state battery has double-interface stability.
The object of the invention is achieved by at least one of the following technical solutions.
The preparation method of the asymmetric lamellar polymer matrix composite solid electrolyte suitable for the 4.5V all-solid-state battery comprises the following steps:
(1) Preparation of the positive electrode side electrolyte layer: adding polyethylene oxide (PEO), polyvinylidene fluoride (PVDF) and lithium bis (trifluoromethanesulfonyl) amide (LiTFSI) into N, N-Dimethylformamide (DMF), stirring, adding an oxide-based ion conductor, dispersing uniformly, adding a functional lithium salt additive to obtain mixed slurry, pouring the mixed slurry into a mold, volatilizing and drying to obtain an electrolyte layer on the positive electrode side;
(2) Preparation of the negative electrode side electrolyte layer: adding polyethylene oxide (PEO) and lithium bis (trifluoromethanesulfonyl) amide (LiTFSI) into N, N-Dimethylformamide (DMF), stirring, adding an oxide-based ion conductor, dispersing uniformly, adding a functional lithium salt additive to obtain mixed slurry, pouring the mixed slurry into a mold, volatilizing and drying to obtain a negative electrode side electrolyte layer;
(3) And (3) superposing the positive electrode side electrolyte layer in the step (1) on the negative electrode side electrolyte layer in the step (2), and carrying out cold pressing treatment to obtain the asymmetric layered polymer matrix composite solid electrolyte applicable to the 4.5V all-solid-state battery.
Further, the mixed slurry in the step (1) comprises the following components in parts by weight:
80-90 parts of polyethylene oxide;
10-20 parts of polyvinylidene fluoride;
40-50 parts of lithium bis (trifluoromethanesulfonyl) imide;
100-150 parts of N, N-dimethylformamide;
10-20 parts of an oxide-based ion conductor;
0-15 parts of lithium salt additive.
Preferably, the mixed slurry in the step (1) comprises the following components in parts by mass:
80 parts of polyethylene oxide;
20 parts of polyvinylidene fluoride;
44.39 parts of lithium bistrifluoromethane sulfonyl imide;
150 parts of N, N-dimethylformamide;
15 parts of an oxide-based ion conductor;
8 parts of lithium salt additive.
Further preferably, the mixed slurry in the step (1) includes, in parts by weight:
80 parts of polyethylene oxide;
20 parts of polyvinylidene fluoride;
44.39 parts of lithium bistrifluoromethane sulfonyl imide;
150 parts of N, N-dimethylformamide;
15 parts of an oxide-based ion conductor;
3 parts of lithium fluoride;
5 parts of difluoro bis (lithium oxalate) phosphate.
Further, the mixed slurry in the step (2) comprises the following components in parts by weight:
90-100 parts of polyethylene oxide;
40-50 parts of lithium bis (trifluoromethanesulfonyl) imide;
100-150 parts of N, N-dimethylformamide;
10-20 parts of an oxide-based ion conductor;
0-15 parts of lithium salt additive.
Preferably, the mixed slurry in the step (2) comprises the following components in parts by mass:
100 parts of polyethylene oxide;
44.39 parts of lithium bistrifluoromethane sulfonyl imide;
150 parts of N, N-dimethylformamide;
15 parts of an oxide-based ion conductor;
8 parts of lithium salt additive.
Further preferably, the mixed slurry in the step (2) includes, in parts by mass:
100 parts of polyethylene oxide;
44.39 parts of lithium bistrifluoromethane sulfonyl imide;
150 parts of N, N-dimethylformamide;
15 parts of an oxide-based ion conductor;
3 parts of lithium fluoride;
5 parts of lithium nitrate.
Further, the oxide-based ion conductors in step (1) and step (2) are both Li 7 La 3 Zr 2 O 12 (abbreviated as LLZO) and its ion doped products.
Preferably, the oxide-based ion conductors of step (1) and step (2) are both Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 。
Further, the lithium salt additive in the step (1) is one or more of lithium fluoride (LiF) and lithium difluorobis (oxalato) phosphate (lidadfp); the lithium salt additive in the step (2) is lithium fluoride (LiF) and lithium nitrate (LiNO) 3 ) More than one of them.
Preferably, in the mixed slurry in the step (1), the mass part of lithium fluoride (LiF) is 0-5 parts, and the mass part of lithium difluorobis (oxalato) phosphate (lidadfp) is 0-10 parts; in the mixed slurry in the step (2), the mass part of lithium fluoride (LiF) is 0-5 parts, and the lithium nitrate(LiNO 3 ) The mass portion of (2) is 0-10.
Further, the temperature of the stirring treatment in the step (1) and the step (2) is 40-60 ℃, and the stirring treatment time is 3-12h;
preferably, the temperature of the stirring treatment in the step (1) and the step (2) is 50 ℃, and the stirring treatment time is 6 hours.
Further, the volatilizing and drying in the step (1) and the step (2) comprises: drying at 40-60deg.C under normal pressure for 2-5 hr, and drying at 50-80deg.C under vacuum for 12-48 hr.
Preferably, the volatilizing and drying in step (1) and step (2) includes: drying at 50deg.C under normal pressure for 3 hr, and drying at 80deg.C under vacuum for 24 hr.
Further, the pressure of the cold press molding in the step (3) is 5-10MPa.
Preferably, the pressure of the cold press molding in the step (3) is 8MPa.
The invention provides an asymmetric lamellar polymer matrix composite solid electrolyte which is applicable to 4.5V all-solid batteries and is prepared by the preparation method.
The asymmetric lamellar polymer matrix composite solid electrolyte suitable for the 4.5V all-solid-state battery can be applied to the preparation of all-solid-state lithium batteries.
The layered polymer-based solid electrolyte prepared by the method can be used in a 4.5V high-voltage all-solid lithium battery, and assembled LiFe x Mn y PO 4 The (x+y=1) -based all-solid battery has dual-interface stability, exhibits high rate capacity and excellent cycle performance.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) The layered composite polymer-based solid electrolyte membrane prepared by the invention has an asymmetric structure, can simultaneously meet different requirements of a high-voltage positive electrode and a metal lithium negative electrode on the polymer-based solid electrolyte, and also has the functions of stabilizing the positive electrode/electrolyte and the negative electrode/electrolyte; in addition, the polymer-based solid electrolyte provided by the invention can be used for a 4.5V high-voltage all-solid-state battery, and the prepared all-solid-state high-voltage lithium battery has higher rate capacity and excellent cycle stability.
(2) The functional lithium salt additive in the positive/negative electrode side electrolyte layer used in the invention has the advantages of low cost, small dosage, simple operation in the whole preparation process and mass production.
Drawings
FIG. 1 is a graph comparing electrochemical stability windows of layered polymer matrix composite solid electrolyte assembled semi-symmetrical cells of example 3, comparative example 1 and comparative example 2;
FIG. 2 is a graph of 0.5mA cm for a polymer-based solid state electrolyte assembled symmetrical cell of example 3 -2 A long-period cycle chart at current density;
FIG. 3 is a polymer-based solid state electrolyte assembled symmetrical cell of comparative example 1 at 0.5mA cm -2 A long-period cycle chart at current density;
fig. 4 is a graph showing comparison of the rate performance of all solid-state batteries assembled from the layered polymer-based composite solid-state electrolytes of examples and comparative examples;
fig. 5 is a graph showing a comparison of long-cycle performance of all solid-state batteries assembled from the asymmetric layered polymer-based composite solid-state electrolytes of examples 1, 2, 3 and 4.
Detailed Description
The following examples are presented to further illustrate the practice of the invention, but are not intended to limit the practice and protection of the invention. It should be noted that the following processes, if not specifically described in detail, can be realized or understood by those skilled in the art with reference to the prior art. The reagents or apparatus used were not manufacturer-specific and were considered conventional products commercially available.
Example 1
A method for preparing an asymmetric layered polymer matrix composite solid electrolyte suitable for a 4.5V all-solid state battery, comprising the steps of:
(1) Weighing 0.8g of polyethylene oxide (PEO), 0.2g of polyvinylidene fluoride (PVDF) and 0.4439g of lithium bistrifluoromethane sulfonyl imide (LiTFSI), addingInto a round bottom flask containing 15g of N, N-Dimethylformamide (DMF), stirring at 50℃for 6h; after formation of a transparent viscous liquid, 0.15g of Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 Uniformly dispersing to obtain brown slurry, weighing LiF (0.03 g), adding into the slurry, and uniformly dispersing; and injecting the slurry which is thoroughly and uniformly dispersed into a mould, firstly drying at 50 ℃ and normal pressure for 3 hours to volatilize the solvent, then transferring into a vacuum drying oven at 80 ℃ for vacuum drying for 24 hours to obtain the electrolyte layer at the positive electrode side, and cutting the electrolyte layer into small wafers with the diameter of 19mm for later use.
(2) 1.0g polyethylene oxide (PEO) and 0.4439g lithium bistrifluoromethane sulfonimide (LiTFSI) were weighed into a round bottom flask containing 15g N, N-Dimethylformamide (DMF) and stirred at 50℃for 6h; after formation of a transparent viscous liquid, 0.15g of Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 Uniformly dispersing to obtain white slurry, and weighing LiF (0.03 g) and LiNO 3 (0.05 g) adding the above slurry, and uniformly dispersing; and injecting the slurry which is thoroughly and uniformly dispersed into a mould, firstly drying at 50 ℃ and normal pressure for 3 hours to volatilize the solvent, then transferring into a vacuum drying oven at 80 ℃ for vacuum drying for 24 hours to obtain the electrolyte layer at the negative electrode side, and cutting the electrolyte layer into small wafers with the diameter of 19mm for later use.
(3) And (3) laminating the positive electrode side electrolyte layer in the step (1) and the negative electrode side electrolyte layer in the step (2), and then performing cold press molding under the pressure of 8MPa to obtain the asymmetric lamellar polymer matrix composite solid electrolyte.
Example 2
A method for preparing an asymmetric layered polymer matrix composite solid electrolyte suitable for a 4.5V all-solid state battery, comprising the steps of:
(1) 0.8g polyethylene oxide (PEO), 0.2g polyvinylidene fluoride (PVDF) and 0.4439g lithium bistrifluoromethane sulfonimide (LiTFSI) were weighed into a round bottom flask containing 15g N, N-Dimethylformamide (DMF) and stirred at 50℃for 6h; after formation of a transparent viscous liquid, 0.15g of Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 Uniformly dispersing to obtain brown colorSlurry, then LiF (0.03 g) and LiDODFP (0.03 g) are weighed and added into the slurry, and the slurry is uniformly dispersed; and injecting the slurry which is thoroughly and uniformly dispersed into a mould, firstly drying at 50 ℃ and normal pressure for 3 hours to volatilize the solvent, then transferring into a vacuum drying oven at 80 ℃ for vacuum drying for 24 hours to obtain the electrolyte layer at the positive electrode side, and cutting the electrolyte layer into small wafers with the diameter of 19mm for later use.
(2) 1.0g polyethylene oxide (PEO) and 0.4439g lithium bistrifluoromethane sulfonimide (LiTFSI) were weighed into a round bottom flask containing 15g N, N-Dimethylformamide (DMF) and stirred at 50℃for 6h; after formation of a transparent viscous liquid, 0.15g of Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 Uniformly dispersing to obtain white slurry, and weighing LiF (0.03 g) and LiNO 3 (0.05 g) adding the above slurry, and uniformly dispersing; and injecting the slurry which is thoroughly and uniformly dispersed into a mould, firstly drying at 50 ℃ and normal pressure for 3 hours to volatilize the solvent, then transferring into a vacuum drying oven at 80 ℃ for vacuum drying for 24 hours to obtain the electrolyte layer at the negative electrode side, and cutting the electrolyte layer into small wafers with the diameter of 19mm for later use.
(3) And (3) laminating the positive electrode side electrolyte layer in the step (1) and the negative electrode side electrolyte layer in the step (2), and then performing cold press molding under the pressure of 8MPa to obtain the asymmetric lamellar polymer matrix composite solid electrolyte.
Example 3
A method for preparing an asymmetric layered polymer matrix composite solid electrolyte suitable for a 4.5V all-solid state battery, comprising the steps of:
(1) 0.8g polyethylene oxide (PEO), 0.2g polyvinylidene fluoride (PVDF) and 0.4439g lithium bistrifluoromethane sulfonimide (LiTFSI) were weighed into a round bottom flask containing 15g N, N-Dimethylformamide (DMF) and stirred at 50℃for 6h; after formation of a transparent viscous liquid, 0.15g of Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 Uniformly dispersing to obtain brown slurry, then weighing LiF (0.03 g) and LiDODFP (0.05 g) and adding into the slurry, and uniformly dispersing; injecting the slurry into a mold, drying at 50deg.C under normal pressure for 3 hr to volatilize solvent, and transferring to 80deg.C under vacuumAnd (3) drying in a drying box for 24 hours in vacuum to obtain the positive electrode side electrolyte layer, and cutting the positive electrode side electrolyte layer into small discs with the diameter of 19mm for later use.
(2) 1.0g polyethylene oxide (PEO) and 0.4439g lithium bistrifluoromethane sulfonimide (LiTFSI) were weighed into a round bottom flask containing 15g N, N-Dimethylformamide (DMF) and stirred at 50℃for 6h; after formation of a transparent viscous liquid, 0.15g of Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 Uniformly dispersing to obtain white slurry, and weighing LiF (0.03 g) and LiNO 3 (0.05 g) adding the above slurry, and uniformly dispersing; and injecting the slurry which is thoroughly and uniformly dispersed into a mould, firstly drying at 50 ℃ and normal pressure for 3 hours to volatilize the solvent, then transferring into a vacuum drying oven at 80 ℃ for vacuum drying for 24 hours to obtain the electrolyte layer at the negative electrode side, and cutting the electrolyte layer into 19mm small wafers for later use.
(3) And (3) laminating the positive electrode side electrolyte layer in the step (1) and the negative electrode side electrolyte layer in the step (2), and then performing cold press molding under the pressure of 8MPa to obtain the layered polymer matrix composite solid electrolyte.
Example 4
A method for preparing an asymmetric layered polymer matrix composite solid electrolyte suitable for a 4.5V all-solid state battery, comprising the steps of:
(1) 0.8g polyethylene oxide (PEO), 0.2g polyvinylidene fluoride (PVDF) and 0.4439g lithium bistrifluoromethane sulfonimide (LiTFSI) were weighed into a round bottom flask containing 15g N, N-Dimethylformamide (DMF) and stirred at 50℃for 6h; after formation of a transparent viscous liquid, 0.15g of Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 Uniformly dispersing to obtain brown slurry, then weighing LiF (0.03 g) and LiDODFP (0.1 g) and adding into the slurry, and uniformly dispersing; and injecting the slurry which is thoroughly and uniformly dispersed into a mould, firstly drying at 50 ℃ and normal pressure for 3 hours to volatilize the solvent, then transferring into a vacuum drying oven at 80 ℃ for vacuum drying for 24 hours to obtain the electrolyte layer at the positive electrode side, and cutting the electrolyte layer into small discs with the diameter of 19mm for later use.
(2) 1.0g polyethylene oxide (PEO) and 0.4439g lithium bistrifluoromethane sulfonimide (LiTFSI) were weighed and added to a flask containing 15g N, N-In a round bottom flask of Dimethylformamide (DMF), stirring at 50℃for 6h; after formation of a transparent viscous liquid, 0.15g of Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 Uniformly dispersing to obtain white slurry, and weighing LiF (0.03 g) and LiNO 3 (0.05 g) adding the above slurry, and uniformly dispersing; and injecting the slurry which is thoroughly and uniformly dispersed into a mould, firstly drying at 50 ℃ and normal pressure for 3 hours to volatilize the solvent, then transferring into a vacuum drying oven at 80 ℃ for vacuum drying for 24 hours to obtain the electrolyte layer at the negative electrode side, and cutting the electrolyte layer into 19mm small wafers for later use.
(3) And (3) laminating the positive electrode side electrolyte layer in the step (1) and the negative electrode side electrolyte layer in the step (2), and then performing cold press molding under the pressure of 8MPa to obtain the layered polymer matrix composite solid electrolyte.
Comparative example 1
Comparative example 1 in comparison with example 3, a polymer-based composite solid electrolyte was obtained by pressing in step (3) in example 3 using two layers of the positive electrode electrolyte layer prepared in step (1) in example 3.
Comparative example 2
Comparative example 2 in comparison with example 3, a polymer-based composite solid electrolyte was obtained by pressing in step (3) in example 3 using two layers of the negative electrode electrolyte layer prepared in step (2) in example 3.
Comparative example 3
Comparative example 3 As compared with example 3, the functional lithium salt additive used in step (2) was LiF (0.03 g), liNO 3 (0.00 g), the other conditions being unchanged.
Comparative example 4
Comparative example 4 As compared with example 3, the functional lithium salt additive used in step (2) was LiF (0.03 g), liNO 3 (0.10 g), the other conditions being unchanged.
The testing method comprises the following steps:
ion conductivity test: after the layered composite electrolyte membrane prepared in the examples and comparative examples of the present invention was sandwiched between two stainless steel gaskets to prepare a button CR2025 type stainless steel/layered electrolyte membrane/stainless steel symmetrical cell, the impedance at different temperatures was tested, and thus the ionic conductivity was calculated, and the results are shown in table 1.
TABLE 1
As is clear from table 1, comparative examples 1, 2, 3 and 4, the ionic conductivity of the layered composite electrolyte membrane increased with an increase in the amount of lithium difluorobis oxalato phosphate added to the positive electrode side electrolyte layer; as is clear from comparative examples 3, 1 and 2, the positive electrode side electrolyte layer has lower ionic conductivity than the negative electrode side electrolyte layer, and at the same time, when the positive electrode electrolyte layer and the negative electrode electrolyte layer are combined, no obvious interface exists between the two layers, so that the ionic conductivity of the prepared asymmetric layered composite electrolyte membrane is still higher; as is clear from comparative examples 3, 3 and 4, the ionic conductivity of the layered composite electrolyte membrane increased with an increase in the amount of lithium nitrate added in the negative electrode side electrolyte layer, however, lithium nitrate itself was unstable at high voltage, and excessive addition was detrimental to the stability of the electrolyte, so that the amount of lithium nitrate added in the negative electrode side electrolyte layer was determined to be 0.05g, and the effect of the amount of lithium difluorobisoxalato phosphate added in the positive electrode side electrolyte layer on the cycle performance of the battery was studied.
Electrochemical stability test: the layered composite electrolyte membrane prepared in the examples and comparative examples of the present invention was sandwiched between a stainless steel gasket and metallic lithium (Li) to prepare a button CR2025 type stainless steel/layered electrolyte membrane/Li semi-symmetrical battery, and then a linear voltammetry test was performed at a voltage ranging from 2.5 to 6.0V under test conditions of 60 ℃ and 5mV/s, and the result is shown in fig. 1. The test result shows that the electrolyte layer on the positive electrode side has a higher electrochemical stability window, so that when the electrolyte layer on the positive electrode side is contacted with the positive electrode, the electrolyte layer on the positive electrode side can be ensured not to be decomposed under the high-pressure condition, thereby avoiding the generation of side reactions of a positive electrode interface, and the shaded part in the figure is the decomposition of the difluoro-lithium bisoxalato phosphate additive in the electrolyte layer on the positive electrode side under the high voltage, thereby indirectly proving that the difluoro-lithium bisoxalato phosphate can form a stable solid film on the surface of the positive electrode through oxidative decomposition.
Lithium stability test: after the layered composite electrolyte membrane prepared in example 3 and comparative example 1 of the present invention was sandwiched between two metal lithium (Li) sheets to prepare a button CR2025 type Li/layered electrolyte membrane/Li symmetric battery, the current density was 0.5mA/cm -2 The symmetric cells were tested for lithium stability at 60 c, and the test results are shown in fig. 2 and 3, which show that although the positive electrode side electrolyte layer has better high-voltage resistance, it has poor lithium stability (fig. 2), whereas the negative electrode side electrolyte layer having poor high-voltage resistance shows better lithium stability, and thus the layered electrolyte prepared by compositing the positive electrode electrolyte layer and the negative electrode electrolyte layer shows excellent lithium stability (fig. 3).
High voltage all-solid-state battery test: the layered composite electrolyte membrane prepared by the examples and the comparative examples of the present invention was sandwiched between LiFe 0.5 Mn 0.5 PO 4 After a button CR2025 type all-solid metal lithium battery was prepared between the positive electrode sheet and the lithium metal (Li) negative electrode, the battery rate performance and cycle stability were tested at 2.5-4.5V, 60 ℃ and different current densities (1c=170ma/g), and as a result, as shown in fig. 4 and 5, the results of fig. 4 indicate that the all-solid battery prepared from comparative example 2 was not basically operated normally (except for the first turn) because the negative electrode side electrolyte layer was not stably operated at a voltage of 4.5V. In contrast, all-solid-state batteries assembled from layered electrolytes formed by compositing a positive electrode electrolyte layer and a negative electrode electrolyte layer can work normally, and as the addition amount of lithium difluorobisoxalato phosphate in the positive electrode side electrolyte layer increases, the rate performance of the battery increases gradually and then decreases sharply, because the surface of the positive electrode is oxidized to form a film too thick (caused by excessive decomposition of lithium difluorobisoxalato phosphate) to prevent the transmission of lithium ions. Therefore, a proper amount of the lithium difluorobis (oxalato) phosphate additive is required in the positive electrode side. Meanwhile, the long-period cycle performance at 1C of examples 1, 2, 3 and 4 confirm the key effect of adding lithium difluorobisoxalato phosphate to the positive electrode electrolyte layer on the cycle performance.
The above examples are only preferred embodiments of the present invention, and are merely for illustrating the present invention, not for limiting the present invention, and those skilled in the art should not be able to make any changes, substitutions, modifications and the like without departing from the spirit of the present invention.
Claims (6)
1. A method for preparing an asymmetric layered polymer-based composite solid electrolyte suitable for a 4.5V all-solid battery, comprising the steps of:
(1) Preparation of the positive electrode side electrolyte layer: adding polyethylene oxide, polyvinylidene fluoride and lithium bistrifluoromethane sulfonyl imide into N, N-dimethylformamide, stirring, adding an oxide-based ion conductor, uniformly dispersing, adding a functional lithium salt additive to obtain mixed slurry, pouring the mixed slurry into a mould, volatilizing and drying to obtain an anode side electrolyte layer;
(2) Preparation of the negative electrode side electrolyte layer: adding polyethylene oxide and lithium bistrifluoromethane sulfonyl imide into N, N-dimethylformamide, stirring, adding an oxide-based ion conductor, dispersing uniformly, adding a functional lithium salt additive to obtain mixed slurry, pouring the mixed slurry into a mould, volatilizing and drying to obtain a negative electrode side electrolyte layer;
(3) Superposing the positive electrode side electrolyte layer in the step (1) on the negative electrode side electrolyte layer in the step (2), and obtaining the asymmetric lamellar polymer matrix composite all-solid electrolyte applicable to the 4.5V solid-state battery through cold pressing treatment;
the mixed slurry in the step (1) comprises the following components in parts by mass:
the functional lithium salt additive in the step (1) is more than one of lithium fluoride and difluoro lithium bis (oxalato) phosphate; in the mixed slurry in the step (1), the mass part of lithium fluoride is 3 parts, and the mass part of difluoro bis (lithium oxalate) phosphate is 3-10 parts;
the mixed slurry in the step (2) comprises the following components in parts by mass:
the functional lithium salt additive in the step (2) is more than one of lithium fluoride and lithium nitrate; in the mixed slurry in the step (2), the mass part of lithium fluoride is 3 parts, and the mass part of lithium nitrate is 5 parts.
2. The method for producing an asymmetric layered polymer matrix composite solid electrolyte suitable for a 4.5V all-solid state battery according to claim 1, wherein the oxide-based ion conductor of step (1) and step (2) are both Li 7 La 3 Zr 2 O 12 And one or more of its ion doped products.
3. The method for preparing an asymmetric layered polymer matrix composite solid electrolyte suitable for a 4.5V all-solid battery according to claim 1, wherein the temperature of the stirring treatment in step (1) and the stirring treatment in step (2) are both 40-60 ℃, and the stirring treatment time is 3-12 hours; the volatilizing and drying in the step (1) and the step (2) comprises the following steps: drying at 40-60deg.C under normal pressure for 2-5 hr, and drying at 50-80deg.C under vacuum for 12-48 hr.
4. The method for producing an asymmetric layered polymer matrix composite solid electrolyte suitable for a 4.5V all-solid state battery according to claim 1, wherein the cold press molding pressure in step (3) is 5 to 10MPa.
5. An asymmetric layered polymer matrix composite solid electrolyte suitable for a 4.5V all-solid state battery, made by the method of any one of claims 1-4.
6. Use of the asymmetric layered polymer matrix composite solid state electrolyte suitable for 4.5V all-solid state batteries as claimed in claim 5 in the preparation of all-solid state lithium batteries.
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